This invention relates to a process for preparing a 3′- or 2′-hydroxymethyl substituted nucleoside derivative, compounds and pharmaceutical compositions for, and a method of treating hepatitis virus infections and/or proliferative disorders in patients using 3′-hydroxymethyl and 2′-hydroxymethyl substituted nucleosides and structurally related nucleosides of general formulas [I]–[IV] and their L-nucleoside counterparts.
wherein the substituents are as defined herein.
Hepatitis B virus (HBV) infection is the most prevalent form of hepatitis and is the second most common infectious disease worldwide. Approximately 5% of the world's population is chronically infected with HBV. The virus is transmitted through blood transfusions, contaminated needles, sexual contact and transmission from mother to child. Moreover, a significant number of people are infected by unknown means.
Carriers of the hepatitis B virus can exhibit various forms of disease, one of which is chronic hepatitis B. Approximately 50% of the carriers show chronic inflammatory changes in the liver and, of these, about 50% have histopathologic changes, which are termed “chronic active hepatitis,” which may lead to fibrosis and ultimately to cirrhosis and progressive liver failure. Carriers without chronic inflammatory changes may also develop chronic active hepatitis, while liver cancer develops in about 10 to 30% of hepatitis B carriers. It has been estimated that approximately 4 million carriers of hepatitis B virus die each year from liver cancer or cirrhosis.
HBV, also known as the Dane particle, is a member of the Hepadonaviridae and is a 42 nm complex spherical particle composed of an outer lipoprotein coat (hepatitis B surface antigen HBsAg) and an inner core (hepatitis B core antigen, HBcAg). (Ganem, D., Fundamental Virology, 3rd Ed., Lippincott-Raven Pub., Philadelphia, 1996, p. 1199) This core contains partially double stranded DNA of 3.2 kb maintained as a circular structure by 5′ cohesive ends. (Chu, C. K., Therapies for Viral Hepatitis, Schinazi, et al., Eds., International Medical Press, 1998) The viral minus strand is full length, while the plus strand is less than full length. The 5′ ends of both strands contain short (11 nucleotide) direct repeats. These repeats are involved in priming the synthesis of their respective strands. Remarkably, viral DNA is synthesized in a reverse transcription of an RNA template. (Mason, W. S., Adv. Virus. Res., 1987, 32, 35) Following viral infection, the viral replication cycle begins with translocation of nucleocapsids from the cytoplasm to the nucleus. (Eckart, S. G., J. Virol., 1991, 65, 575) The partially duplex genomic DNA is converted to fully duplex covalently closed supercoiled DNA, which persists as an episomal minichromosome and functions as a reservoir of the viral genome. This feature provides a difficult challenge to therapeutic attack on the virus.
The episomal DNA is transcribed by the host RNA polymerase II and viral proteins are translated from the transcription products. Among the transcripts are full length pregenomic RNAs which are encapsulated by the viral structural proteins together with the viral polymerase. Synthesis of both viral DNA strands by the viral polymerase occurs within these structures. The polymerase contains both a reverse transcriptase and an RNAse H domain. Minus strand synthesis proceeds in two distinct steps (Zolim, F., J. Virol., 1994, 68, 3536). In the first, the polymerase binds to the direct repeat at the 5′ end of the pregenomic RNA and serves as a covalent primer for the synthesis of a 4 nucleotide element. The priming hydroxyl group is the side chain of a tyrosine residue on the polymerase and is linked to a dGMP residue. A sequence in the bulge of a stem loop structure in the RNA template serves as the template for this step. This reaction is particular to the virus and is not mimicked in any cellular DNA synthesis reaction. Agents which target this step would have the potential for a high degree of specificity. Following this step the polymerase-nucleotide complex translocates to the other end of the RNA template and complete reverse transcription of the strand takes place. (It has been proposed that there may be proteolytic cleavage of polymerase and RNAse domains away from the portion of the polymerase bound to the tetranucleotide primer. (Bartenschlager, R., EMBO J. 1988, 7, 4185). First strand synthesis is accompanied by the degradation of the RNA in the RNA:DNA hybrid by the RNAse H of the polymerase. Synthesis of the second strand, also mediated by the viral polymerase, is generally incomplete, giving rise to the partially duplex DNA found in the virion.
It is now clear that there are three separate phases in replication and that the first reverse transcription step is of particular interest for therapeutic intervention. It should be noted that an agent that inhibits the reverse transcriptase of other retroviruses does not necessarily have activity against HBV. For example, Zidovudine (or AZT) as its 5′-triphosphate is a potent inhibitor of reverse transcriptase of human immunodeficiency virus and has been widely used in the treatment of HIV-infected patients. However, this agent is inactive against HBV. On the other hand, certain 2′-fluoro-D-arabino nucleosides, such as Fiacitabine (FIAC) and Fialuridine (FIAU), are devoid of activity against HIV although they effectively inhibit replication of HBV.
Hepatitis C virus (HCV), the second major cause of viral hepatitis, is present in an estimated 170 million carriers worldwide, 3.9 million of whom reside in the United States. HCV is considered the most common blood-borne infection in the United States, where it is one of the leading causes for liver transplantation among adults. Most people infected with HCV do not exhibit any acute signs or symptoms of hepatitis. In fact, unless they have a blood test, most people remain unaware that they are infected with HCV for the first 10–20 years.
Aside from direct blood contact, HCV is a very difficult agent to transmit. Maternal-to-fetal transmission is quite low, less than 6% of babies born to infected mothers will carry the virus. Additionally, unlike HBV and human immunodeficiency virus (HIV), evidence of direct sexual transmission of HCV is inconclusive.
HCV is a small, enveloped virus in the Flaviviridae family, with a positive single-stranded RNA genome of ˜9.6 kb within the nucleocapsid. The genome contains a single open reading frame (ORF) encoding a polyprotein ofjust over 3,000 amino acids, which is cleaved to generate the mature structural and nonstructural viral proteins. ORF is flanked by 5′ and 3′ non-translated regions (NTRs) of a few hundred nucleotides in length, which are important for RNA translation and replication. The translated polyprotein contains the structural core (C) and envelope proteins (E1, E2, p7) at the N-terminus, followed by the nonstructural proteins (NS2, NS3, NS4A, NS4B, NS5A, NS5B). The mature structural proteins are generated via cleavage by the host signal peptidase. The junction between NS2 and NS3 is autocatalytically cleaved by the NS2/NS3 protease, while the remaining four junctions are cleaved by the N-terminal serine protease domain of NS3 complexed with NS4A. The NS3 protein also contains the NTP-dependent helicase activity which unwinds duplex RNA during replication. The NS5B protein possesses RNA-dependent RNA polymerase (RDRP) activity, which is essential for viral replication. It is emphasized here that, unlike HBV or HIV, no DNA is involved in the replication of HCV. Recently in in vitro experiments using NS5B, substrate specificity for HCV-RDRP was studied using guanosine 5′-monophosphate (GMP), 5′-diphosphate (GDP), 5′-triphosphate (GTP) and the 5′-triphosphate of 2′-deoxy and 2′,3′-dideoxy guanosine (dGTP and ddGTP, respectively). The authors claimed that HCV-RDRP has a strict specificity for ribonucleoside 5′-triphosphates and requires the 2′- and 3′—OH groups. Their experiments suggest that the presence of 2′- and 3′-substituents would be the prerequisite for nucleoside 5′-triphosphates to interact with HCV-RDRP and to act as substrates or inhibitors. The present invention on the development of anti-HCV agents is based on this rationale.
Hepatitis D virus (HDV) is classified separately from other hepatitis viruses, but it is often found in association with hepatitis B virus. The host range of HDV is limited to those species that support the replication of a hepadnavirus capable of supplying a helper function. These include the chimpanzee (hepatitis B virus), the eastern woodchuck (woodchuck hepatitis virus) and possibly the Pekin duck (duck hepatitis virus). The successful replication of HDV is dependent on the replication of the helper hepadnavirus. Inhibition of hepatitis B virus, therefore, should result in inhibition of HDV. Also, while HDV appears to employ the host RNA polymerase, it is not clear if the virus causes some modification of the polymerase enabling it to replicate the HDV genome more efficiently. Thus, nucleosides that inhibit the HBV polymerase or the modified host RNA polymerase would be expected to inhibit the replication of HDV.
The synthesis of some related compounds has been disclosed in the literature (Acton, E. M., et al., J. Med. Chem., 1979; 22:518; Fiandor, J., et al., Nucleosides Nucleotides, 1989; 8:1107; Bamford, M. J., et al., J. Med. Chem., 1990; 23:2494; Svansson, L., et al., J. Org. Chem., 1991; 56:2993; Sterzycki, R. Z., et al., Nucleosides Nucleotides, 1991; 10:291; Svansson, L., et al., Nucleosides Nucleotides, 1992; 11:1353; Kvamstrom, I., et al., Nucleosides Nucleotides, 1992; 11:1367; Tseng, C. K-H., et al., J. Med. Chem., 1991; 34: 343; Lin, T-S., et al., J. Med. Chem., 1993; 36:353; Wengel, J., et al., Bioorg. Med. Chem., 1995; 3:1223; Lee-Ruff, E., et al., J. Med. Chem., 1996; 39:5276; Jorgensen, P. N., et al., Nucleosides Nucleotides, 1997; 16:1063; Jeong, L. S., et al., Nucleosides Nucleotides, 1997; 16:1059;). Moreover, these references also disclose anti-viral test results of some of these compounds against herpes virus (HSV) or human immunodeficiency virus (HIV). Only 2′,3′-dideoxy-3′-hydroxymethyl-cytidine and adenosine show good activity against HIV and 2′,3′-dideoxy-3′-hydroxymethyl-cytidine (Sterzycki, R. Z., et al., Nucleosides Nucleotides, 1991, 10, 291) and 5-bromovinyl-1-(3-deoxy-3-hydroxymethyl-D-arabinofuranosyl)-uracil (Svansson, L., et al., J. Org. Chem., 1991, 56, 2993) are active against HSV.
Although it would not have been expected that an anti-herpes virus agent or anti-HIV agent would also be effective in the treatment of hepatitis, the compounds of the present invention have surprisingly been found to be useful as anti-hepatitis agents. Some of these compounds are particularly favorable in the treatment of hepatitis because they unexpectedly cause less toxic side effects. For example, we discovered that 3′-deoxy-3′-hydroxymethylthymidine, which, though devoid of activity against murine leukemia virus (MuLV), HIV, HSV-1, HSV-2, human cytomegalovirus (HCMV), Varicella zoster virus (VZV) and Epstein Barr virus (EBV)( Sterzycki, R. Z., et al., Nucleosides Nucleotides, 1991, 10, 291), is a potent agent against HBV.
It is therefore an object of the present invention to provide compounds and compositions useful for the treatment of hepatitis.
It is a further object of the present invention to provide a method for treating hepatitis using the compounds of the present invention.
It is another object of the present invention to provide compositions for treating hepatitis comprising the compounds of the present invention in combination with other anti-hepatitis agents.
It is another object of the present invention to provide a method for treating hepatitis using the compounds of the present invention in combination with other anti-hepatitis agents.
It is still another object of the present invention to provide compounds and compositions useful for the treatment of proliferative disorders.
It is still another object of the present invention to provide a method for treating proliferative disorders using the compounds of the present invention.
It is still another object of the present invention to provide a process for preparing 3′- or 2′-hydroxymethyl substituted nucleoside derivatives.